I posted this on another thread, so I'm pasting it here rather then re-explaining it again.
Cardio and protein and carbs.
As far as fasted cardio - it matters how you execute it. Duration, intensity, pre and post nutrition, etc. In a muscle sparing sense, you want to be getting protein into you, post a fasted cardio session, otherwise you will lose muscle. But having CHO immediately after a cardio session is probably a bit of a waste as you were doing, as that would stop the fat burning process.
Yes - eating protein right after training or cardio stops catabolism, but allows fat burning to continue unabated. As soon as you add carbs, in a continuum sense, you slow down/stop fat usage and even create fat storage. The other side of the coin with carbs is that they ARE the anabolic factor, so after training, you should have some even when dieting.
I'd use very small amounts of carbs and BCAAs before morning cardio; small being 10-15 grams. And, not all cardio has to be in the a.m.; the benefits to that have some cons as well – such as losing muscle as I mentioned. I would never do high-intensity cardio in the morning.
If it’s in the afternoon, depends on the structure of the whole morning, but for 15-20 minutes of higher-intensity cardio, you won't need much food (since you would have had a meal or two already). Blood sugar/liver glycogen alone will keep you from crashing...BUT, I'd have a little something just prior in order to make sure you had that initial burst. If you had normal meals at 6:00 and 9:00, for example, and you were doing cardio at noon; at about 11:30 I'd have about 1/4 c of oats and 2 scoops of BCAAs or a rice cake, 1 tbsp PB and the BCAAs, then do the cardio, then eat a mostly-protein/fibrous vegetable lunch, then the next meal normal. That is, of course, if you're using the cardio as part of weight loss. If you're in the off-season, I'd go ahead and have a normal amount of carbs/starch at lunch but still keep the pre-cardio stuff the same.
I forgot to add. Once you have the protein immediately after cardio, you can have a regular meal containing protein and cho 1 1/2-2 hours later. I usually have it 1 to 1.5 hours later bc I'm very hungry in the morning. I don't feel satisfied till about my 4th meal.
I hope that helps..